The present invention relates to a method and apparatus for stripping the insulation from a segment of indeterminate length wire in connection with winding machines for forming stator coils.
In the manufacture of electric motors and other dynamoelectric machines, the excitation windings are usually made of magnet wire comprising a copper or aluminum core covered with a suitable layer of insulation, which may comprise a very thin coating of varnish or polyester resin. The wire is fed into the winding machine, formed into coils, as by the wind and shed technique, for example, and inserted into the slots of the stator core. Winding machinery of the wind and shed type is well known, and is described in the following exemplary U.S. patents, which are expressly incorporated herein by reference: Lauer et al. U.S. Pat. No. 3,977,444; Arnold et al. U.S. Pat. No. Re. 29,007; Cutler et al. U.S. Pat. No. 3,672,026; Arnold U.S. Pat. No. 3,672,027; Cutler et al. U.S. Pat. No. Re. 27,415; Smith U.S. Pat. No. 3,510,939; Lauer U.S. Pat. No. 3,765,080; Lauer U.S. Pat. No. 3,579,791; Smith U.S. Pat. No. 3,514,837; Arnold et al. U.S. Pat. No. 3,973,601; and Arnold U.S. Pat. No. 3,967,658.
During or after the winding process, the wire is cut at one or more places so as to produce a plurality of free ends. The wire ends are connected to a lead set, other motor windings, or terminal devices. Before the connections can be made, however, it is necessary to remove the insulation from the wire. One prior art technique for removing the insulation is that of brazing wherein the operators twist the wire ends around whatever they are to be connected and then heat them with a small torch, at the same time touching the heated wire and other wire or connection device with silver solder. The torch burns away the insulation, while at the same time melting the solder so that a good solder connection is established. As electric motor technology has become more sophisticated, however, insulation materials have been developed which can withstand much higher temperatures, even exceeding the temperature produced by the torch. As a result, the copper or aluminum core of the wire is melted before the insulation so that all that remains is a very fine tubular segment of insulation having no conductive material therein. Obviously, this prevents the establishment of electrical conduction between the wire and the connection device.
Another prior art technique for making electrical connections to the wire ends is to utilize crimp connection devices, which pierce the insulation and make contact with the conductive core of the wire. Examples of this technique are disclosed in U.S. Pat. Nos. 3,505,720 (Heimbrock) and 3,962,780 (Kindig). There have been substantial problems of reliability with crimp connection devices, however, particularly in demanding applications wherein it is necessary for the connections to maintain very good conductivity over a long period of time.
In order to avoid the reliability problems of crimp connection devices, it has often become necessary to use mechanical, hand-operated insulation strippers which strip off the insulation by scraping or cutting action. One such device is disclosed in U.S. Pat. No. 4,117,749 (Economu). It is also known to use small, hand-held strippers wherein a plurality of rotating blades driven by, for example, a pneumatic motor, spin around the wire and cut the insulation from a segment thereof. In this case, the operator manually feeds the free end of a coil lead into the rotating blades, which pivot inwardly and engage the enamel on the wire. Then, as the operator withdraws the end of the wire from the rotating blades, the insulation is cut and removed therefrom. This technique, although suitable for larger diameter wires, does not perform satisfactorily with fine wire, for example, wire finer than 0.025 inch in diameter. Furthermore, this technique does not lend itself to automation, and requires a certain amount of machine down time as the operator locates, inserts and then withdraws the cut ends of the coils.
A more automatic version of the rotating blade stripper is manufactured by The Eraser Company, Inc., of Syracuse, N.Y. In this apparatus, the wire is fed through the center of the machine and advanced through the center of the rotating stripper blades by means of an automatic clamp device which grips the wire and moves it a predetermined distance. The cutter blades are mounted on individual axes and caused to rock inwardly by means of a cam-like thrust block which is rotating in synchronism with the blades and is pressed axially against complementary cam surfaces on the blades so as to cause them to pivot inwardly. The depth of cut is controlled by adjusting the axial distance through which the thrust block is moved by a pneumatic piston and cylinder.
It is a general object of the present invention to provide a method and apparatus wherein insulated magnet wire being fed to a coil winding machine has the enamel insulation effectively stripped therefrom along a desired segment of the wire.
It is another object of the present invention to provide a method and apparatus for stripping wire which is being supplied to a coil winding machine whereby the length and position of the segment of wire which is stripped is automatically controlled so that the stripped segment will be positioned within the wire cutter at the conclusion of the winding cycle.
It is yet another object of the present invention to provide an apparatus for stripping wire which can easily be incorporated into the wire feed paths of existing coil winding machines.
It is a further object of the present invention to provide a method and apparatus for stripping the insulation off wire by means of rotating blades wherein the wire is tensioned and maintained in the center of the blades so as to avoid breaking and deforming the wire.
A still further object of the present invention is to provide a method and apparatus for stripping wire being fed to a coil winding machine wherein the wire is pulled through a stripper device by the winding head without the necessity for additional apparatus and without the necessity for intervention by the machine operator.